There are plenty of things you can do to maximize your ‘up’ time though – if all you need is to be contactable by SMS or phone, well, you can dim the brightness, kill your mobile data, WiFi, Bluetooth and anything else that may drain your juice. If you need music on the move, get yourself a separate music player, such as an iPod shuffle, rather than relying on your mobile phone.

Other than that, you can gain juice with a portable battery pack.

A personal favorite of mine is the PowerGen Mobile Juice Pack, it comes with a built-in micro-USB cable for compatible devices, though you can charge any device with it through the baked-in USB port. You should get at least one full charge and, for less than $20, it’s good value.

If carrying an extra gadget doesn’t appeal, then you could spend a bit more money on something like the Mophie Juice Pack for the Samsung Galaxy S4.

This is the latest upgrade from Mophie, following the version it launched previously for the Samsung Galaxy S3. It’s a case and charger in one, so when your device runs out, you simply flick a switch on the case and your pocket rocket starts to replenish. Mophie offers similar cases for iPhone too.

Hands-on with the Mophie Juice Pack (SGS4)

The Mophie comes in a compact box, and contains two key ingredients – the Mophie Juice Pack itself, and the standard micro-USB cable.

The case is basically an empty shell with a detachable top section that lets you slide your phone in and onto the charging port.

On the back, you’ll see a hole for the camera lens, and at the bottom there’s a button, four little lights and a switch.

The button lets you see roughly how much juice there is left in the case – basically whether it’s flat, a quarter, half, three-quarters or completely full.

When your phone runs out of juice, you simply flick the little switch to the left, and it will automatically start charging your phone.

In terms of size, the Mophie case is bigger than your average case, but given that it houses a 2300 mAh battery, that’s to be expected.

On that note, the case promises to give you roughly 80% charge (see our results below), which makes sense given it’s marginally less powerful than the 2600 mAh battery that ships with the Galaxy S4.

You can see below the extra size the Mophie case adds compared to a standard ‘slim’ S4 case. But given you’re already carrying a pretty chunky device around with you, this may not make much of a difference to you.

The phone slides solidly into the case, and as with a normal charger you can use the phone while its replenishing, or switch it off to maximize the charge.

So that’s what you get, and that’s what it looks like. But how does it perform? Read on.

The verdict

The Mophie Juice Pack is a solid ‘case’ – it doesn’t feel cheap. The speakers, camera, headphone socket, power and volume control all align perfectly with it. Also, if you have the phone in the case and plugged into the charger, you can still charge the phone directly – once it’s full, the charge is then redirected to the case.

We found that the case took just under 2 hours to charge fully from flat, which is acceptable. We also let the Galaxy S4 drain completely to see how much it would charge from flat – on the first attempt it managed 76%, and on the second it notched up 78%. So it’s roughly in line with what Mophie promises.

The downside, of course, is the price. But if you have cash to burn and don’t mind a little extra weight and girth on your handset, $100 might be a drop in the ocean for the convenience of a single case/battery pack in one.

And this is a point worth stressing – it is convenient. With my existing battery pack, I often have it dangling from my phone while browsing the Web or talking to someone – I’m happy to tolerate this minor inconvenience given that it only cost me $20 and it gives me a FULL charge.

The Mophie is a fantastic, well-built piece of kit but weighing the price up against the amount of extra juice it will give you, this may deter those planning a jaunt into the wild for a few days.

If you have the cash and all you’re looking for is a solid case with extra power to see you through the best part of another day, you’ll find this is money well-spent.